Merrill, Michigan Weather Forecast Discussion

073
FXUS63 KDTX 101902
AFDDTX
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
302 PM EDT Wed Sep 10 2025
.KEY MESSAGES...
- Pleasant, dry September weather through Friday.
- Chance of showers and slight chance of thunderstorms Saturday.
&&
.DISCUSSION...
Occasional mid and high clouds will affect Se Mi during the rest of
the day and into tonight as a mid to upper level short wave advances
across Lower Mi. Weak subsidence below 12k feet will sustain a
formidable mid level dry layer and thus inhibit any rain. The high
clouds and slightly higher sfc dewpoints will hold min temps largely
in the 50s tonight. Mid level anticyclonic vorticity advection will
occur across Se Mi Thurs in the wake of the upper level short wave.
This will drive some southward expansion of the large sfc high
pressure system over nrn Ontario into the southern and eastern Great
Lakes Thursday into Friday, allowing a persistence of dry and stable
conditions. The high will force a more NNE wind direction on
Thursday. The 12Z model suite does remain consistent in supporting
weak overall cold air advection. Diurnal heating will easily boost
Thurs highs around 80, with a little stronger onshore flow keeping
the thumb region several degrees cooler. Light southerly flow and
respectable mixing depths will warrant afternoon highs into the low
to possibly mid 80s Friday. Fog may be of concern Thurs night/Fri
morning across the Thumb and Monroe County as the wind fields will
drive the marine layer inland.
A strengthening low to mid tropospheric frontal response is forecast
from nrn Wisconsin into Lower Mi Fri night into Saturday. The 12Z
NAM indicate a brief period of quite good system relative ascent up
the frontal slope with a notable region of instability shown to be
driven into the frontal system along the nose of the low level jet.
While there is still variability among timing and position of the
strongest fgen response, a chance of showers will remain warranted
in the forecast Saturday.
The medium range model suite have been showing a strong mid level
low dropping from Hudson Bay across Quebec and the eastern Great
Lakes into the mid Atlantic in the Sunday to Monday time frame. The
deterministic Canadian and ECMWF have been stronger and farther east
with this wave in comparison to the GFS. The main impact being the
deterministic ECMWF and Canadian drive slightly cooler air into Se
Mi. Ample spread still exists among the ensemble members, leading to
some uncertainty as to whether Sun/Mon highs will remain in the 70s
or 80s. There is high confidence of a dry forecast as strong high
pressure settles across the region. Strong mid level ridging is
forecast to expand into the Great Lakes early next week, offering a
potential warming trend. This may be somewhat mitigated by low level
easterly flow off the lakes.
&&
.MARINE...
An extended stretch of favorable marine conditions continues through
early next week as high pressure expands from Canada into New
England. Light SW winds become NE by Thursday morning as the high
expands south, with the most abrupt wind shift occurring over
northern Lake Huron tonight as remnants of a frontal zone wash out.
Winds follow a steady veering trend Thursday, gradually returning to
the SW by Friday. The return of SW flow aids in moisture transport,
drawing elevated portions of a warm front into the Great Lakes
Saturday and generating a chance for showers. Another surface high
then builds over Ontario early next week with additional support
aloft as upper level ridging slides overhead.
&&
.PREV DISCUSSION...
Issued at 142 PM EDT Wed Sep 10 2025
AVIATION...
VFR conditioned expected through the taf forecast. High pressure
will remain over the area while a stalled front washes out over
northern Michigan and Wisconsin. Upper level system providing
moisture in an otherwise very dry atmosphere creating a mid/high
cloud deck to contend with into tonight. Winds will be light and
variable tonight before emerging out of the southwest on Thursday.
THRESHOLD PROBABILITIES...
* None
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&
$$
DISCUSSION...SC
MARINE.......MV
AVIATION.....DRK
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NWS DTX Office Area Forecast Discussion